Upstream migration of avulsion sites on lowland deltas with river-mouth retreat
Upstream migration of avulsion sites on lowland deltas with river-mouth retreat
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DOI：
10.1016/j.epsl.2021.117270
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发表时间：
2022-01
影响因子：
5.3
通讯作者：
Jiaguang Li;V. Ganti;Chenglong Li;Haoming Wei
中科院分区：
文献类型：
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作者：
Jiaguang Li;V. Ganti;Chenglong Li;Haoming Wei
河流三角洲是肥沃的、人口众多的景观，它们是通过河流崩解而生长的，这是断断续续的河道跳跃事件。从历史上看，三角洲的撕裂经常发生在一些地方，造成了一些有记录以来最致命的洪水。气候变化和人类活动正威胁着淹没三角洲，但目前尚不清楚侵蚀将如何应对，因为它们很少发生在大型低地三角洲。本文以柴达木盆地湖岸形成的低梯度河三角洲为研究对象，探讨了低梯度河三角洲在相对海平面加速上升过程中对河口退缩的响应。利用1973 - 2010年的卫星影像资料，对苏棱郭勒河三角洲6次叶尺度侵蚀对柴达木盆地北霍勒逊湖季节性扩张的响应进行了识别和分析。结果表明，季节性湖水面积的增加导致了断续的河口退缩。因此，崩裂遗址以相应的速率向上游迁移，使得崩裂遗址到河口的顺流距离与回水长度保持一致并呈比例，类似于大型低地三角洲。结果表明，相对海平面上升加速导致的低地三角洲淹没，将使崩解灾害向上游转移数十至数百公里，使新的上游社区面临灾难性洪水的风险。
River deltas are fertile, populous landscapes that grow through river avulsions—episodic channel-jumping events. Historically, avulsions on deltas occurred at persistent locations, causing some of the deadliest recorded floods. Climate change and human activities are threatening to drown deltas but it is unknown how avulsions will respond because they occur infrequently on large, lowland deltas. Here, we use a low-gradient river delta formed on the margin of a lake in the Qaidam Basin, China, as a natural laboratory to explore how lowland deltas will respond to river-mouth retreat from accelerated relative sea-level rise. Using satellite imagery from 1973 to 2010 C.E., we identified and analyzed the response of 6 lobe-scale avulsions on the Sulengguole River delta to the seasonal expansion of the North Huoluxun Lake in the Qaidam Basin. We show that the seasonal lake-water area increase caused punctuated river-mouth retreat. In response, avulsion sites migrated upstream at a commensurate rate such that the avulsion length—streamwise distance of avulsion site to the river mouth—remained consistent and scaled with the backwater lengthscale, similar to large, lowland deltas. Results indicate that the drowning of lowland deltas from accelerated relative sea-level rise will shift avulsion hazards tens-to-hundreds of kilometers upstream, exposing new upstream communities to the risk of catastrophic flooding.